It is known that flat surfaces having a series of folding lines such as to confer them a general shape like an "accordion", also called waviness hereinbelow, cannot be closed on themselves perpendicularly to the folding lines without distortion.
It has now been found a method of folding which allows said wavy plane surfaces to be closed on themselves and moreover to be angled in different ways in the space without any consequent deformation and/or distortion of the waviness.